Is Sphene a single AI or were there two of them?

[Cilia]

There's only one Sphene we interact with throughout Dawntrail: an AI replica modeled on the living Sphene's memories, modified to prioritize Alexandria's preservation and the happiness of its citizens over all else. There's two layers to her - the memories and the programming - in constant competition throughout Dawntrail until her programming determines that her memories (personality) are detrimental to her purpose and she can't emotionally handle the grief and guilt it entails.

It is heavily implied that Sphene wants to stop but due to her personality and programming is unable to do so, so she names us her executioner and spirits everyone else away because she knows the PC is capable of defeating her. Never stated verbatim, but reading between the lines a little...

[Carin-Eri]

There's only one Sphene we interact with throughout Dawntrail: an AI replica modeled on the living Sphene's memories, modified to prioritize Alexandria's preservation and the happiness of its citizens over all else. There's two layers to her - the memories and the programming - in constant competition throughout Dawntrail until her programming determines that her memories (personality) are detrimental to her purpose and she can't emotionally handle the grief and guilt it entails.

It is heavily implied that Sphene wants to stop but due to her personality and programming is unable to do so, so she names us her executioner and spirits everyone else away because she knows the PC is capable of defeating her. Never stated verbatim, but reading between the lines a little...

This. I recall dialogue that stated that when she was brought back as an Endless she was modified by Preservation to prioritize the wellbeing Alexandrian people above all else, without any real regard for how that might affect others. Which was also why she couldn't accept any alternative to Preservation's aether-plundering.

[Brightamethyst]

There's only one Sphene we interact with throughout Dawntrail: an AI replica modeled on the living Sphene's memories, modified to prioritize Alexandria's preservation and the happiness of its citizens over all else. There's two layers to her - the memories and the programming - in constant competition throughout Dawntrail until her programming determines that her memories (personality) are detrimental to her purpose and she can't emotionally handle the grief and guilt it entails.

It is heavily implied that Sphene wants to stop but due to her personality and programming is unable to do so, so she names us her executioner and spirits everyone else away because she knows the PC is capable of defeating her. Never stated verbatim, but reading between the lines a little...

Pretty much this. Sphene is a single entity at odds with itself. The top level "Queen Sphene" personality doesn't like what her underlying programming sometimes forces her to do, but she's essentially powerless to stop it.

And then the WoL came along and she finally saw a way out.